Components such as tools on earth moving equipment, undercarriage components for heavy equipment, pump shafts, engine components, bushings, and other parts with one or more surfaces that undergo contact and relative motion with respect to other surfaces may be subjected to wear and the progressive loss of material. Wear to contacting surfaces may result from abrasion, impact, erosion, galling, cavitation, and other static and/or dynamic conditions, potentially leading to a requirement for repair or replacement of the component more frequently than would otherwise be necessary. Hardfacing is a form of surfacing that may be applied to such wear components for the purpose of reducing the wear and other detrimental surface conditions.
Hardfacing is a metalworking process where harder or tougher material is applied to a base metal. The harder or tougher material may be welded to the base material, and generally takes the form of specialized wire electrodes for arc welding or filler rod for oxyacetylene or tungsten inert gas (TIG) welding. Hardfacing may be applied to a new part during production to increase its wear resistance, or it may be used to restore a worn-down surface. Hardfacing by arc welding is a surfacing operation to extend the service life of industrial components, pre-emptively on new components, or as part of a maintenance program. Hardfacing has resulted in significant savings in machine down time and production costs in many industries.
The American Welding Society defines hardfacing as “[a] surfacing variation in which surfacing material is deposited to reduce wear.” The term surfacing is defined as “[t]he application by welding . . . of a layer, or layers, of material to a surface to obtain desired properties or dimensions, as opposed to making a joint.” AWS A3.0 Standard Welding Terms and Definitions. Hardfacing involves the deposition of a new material on the base material of the component. In general, the hardfacing material may have a similar or a different composition than the base material. Hardfacing may be performed using a number of welding (or cladding) techniques. These techniques can be broadly classified into three categories as, arc welding (or arc cladding), thermal spraying, and laser-based cladding.
There are a number of different arc welding techniques that are commonly used in the industry to perform hardfacing. These include, for example, gas tungsten arc welding (GTAW), plasma arc welding (PAW), plasma transferred arc (PTA), gas metal arc welding (GMAW), submerged arc welding (SAW) and several others. In these processes, an arc is established to melt the surface of the base material, usually in the presence of a shield gas. The hardfacing material, which is introduced in either wire or powder form, is also melted by the arc to form the hardfaced layer. Arc welding produces a layer that is fully welded and metallurgically bonded to the substrate of the component. This layer may have a higher hardness, and therefore better wear properties, than the component substrate. However, a major disadvantage of arc welding is that the high temperatures involved in depositing the hardfaced layer may act to soften (or reduce the hardness of) a layer of material on the surface of the component beneath the hardfaced layer. This zone of heat-softened material on the component surface is referred to as the heat affected zone (HAZ). Therefore, although arc welding deposits a layer of material having high wear resistance on the component surface, the wear resistance of the underlying component surface deteriorates as a result of the heat-intensive welding process. Since the hardfaced layer will eventually wear off after extended operation, reduced wear resistance of the underlying component surface detrimentally affects the useable life of the component by hastening component wear after the hardfaced layer has worn off. Also, in some circumstances, a relatively soft under-layer can also cause the hardfaced layer to be crushed or it can crack as the under-layer gives way. The damaged hardface layer will then spall off the component surface. In addition, during the hardfacing process, the substrate will act like a heat sink and will quench the hardface layer on the surface. When components hardfaced using these traditional techniques are subjected to higher impact abrasive environments, the brittle, hardfaced layer often chips and spalls.
U.S. Pat. No. 2,249,629 issued to Hopkins (the '629 patent) discloses an armored article in which an armor metal is produced by fusing together a hard metal with a base metal using electric energy discharge. After the fusing operation, the armored article is subject to heat treatment to develop the desired hardness in the hard metal and the base metal. The '629 patent disclosed steel chemistry ranges for the base material and heat treatment parameters that would yield base material hardness of 200 to 400 Brinell (approximately Rkw C 18 to 43). While the process of the '629 patent includes heat treatment after a welding operation, this process may have deficiencies. For instance, the heat affected zone (HAZ) created by the welding process may not be restored by the process of the '629 patent. Moreover, the conventional hardfacing electrodes are often very expensive, and have very poor weldability/stability, producing large amounts of spatter and often weld cracking.
The disclosed hardfacing process and products are directed at overcoming these and/or other shortcomings in existing technology.